I say, Watson,’ he whispered, ‘would you be afraid to sleep in the same room as a lunatic, a man with softening of the brain, an idiot whose mind has lost its grip?’ ‘Not in the least,’ I answered in astonishment. ‘Ah, that’s lucky,’ he said, and not another word would he utter that night.

He had maintained a platonic relationship with Jean while his first wife was still alive out of loyalty to her. A sequel to A Study in Scarlet was commissioned and The Sign of the Four appeared in Lippincott's Magazine in February 1890 under agreement with the Ward Lock company. Conan Doyle fathered five children.

He was a prolific writer whose other works include fantasy and science fiction stories plays romances poetry non-fiction and historical novels.